The primary objective of the research program presented below is to examine the genetic control of meiotic recombination, chromosome segregation and ascospore formation during sporulation of yeast. The aim of the research program is to identify loci that govern genetic exhange and the meiotic divisions, and the manner in which mutation of these loci affect the onset and progress of genetic recombination in different intervals of the chromosomal genome, and the cytological landmark events of the sporulation process. For these studies three phenotypic classes of mutants will be isolated: 1) spy mutants -mutants capable of sporulation that produce inviable ascospores when sporulation has occurred at a restrictive temperature, 2) rem mutants -sporulation proficient mutants defective in both spontaneous gene mutation and recombination and 3) rec mutants - mutants defective in meiotic intergenic recombination. Mutants of these three phenotypic classes in conjunction with sporulation-deficient mutants (spo) already under study provide a means of identifying loci required for normal recombination and chromosome segregation as well as ascospore formation following meiosis.